The present invention relates to air conditioners, and in particular to a method for operating a vehicle-mounted air conditioner by conserving the energy of a compressor that supplies pressurized refrigerant to the evaporator. The invention also relates to a vehicle-mounted air conditioner having a power saving compressor control circuit.
Conventionally, vehicle-mounted air conditioners comprise a compressor which, when powered by the vehicle engine, supplies pressurized refrigerant to an evaporator, a heating unit supplied with heated water from the engine cooling system for heating air cooled by the evaporator, and a mixing damper pivotally mounted upstream of the heating unit to adjust the amount of cooled air presented to the heating unit in relation to the amount of cooled air directed toward the interior of the vehicle. The compressor is controllably coupled to the engine output shaft when the vehicle interior temperature demands an increase in cooling capacity, or decoupled from the engine when the interior temperature indicates that the cooling capacity be decreased. Although this compressor control strategy is advantageous in saving energy, there is an undesirable sharp variation in the interior temperature at the instant the compressor operating state is changed.
To overcome this problem Japanese Pat. No. 54-12692 discloses a control system which involves the use of a temperature sensor located downstream of the evaporator for sensing the temperature of cooled air. The resistance of this temperature sensor increases when the compressor is shut off and this increase in resistance is detected by a comparator which in turn operates the mixing damper in a direction that reduces the amount of cool air presented to the heating unit in relation to the amount of cool air directed to the vehicle interior.